Electric resistor



P 6 1955 H. E. HOLLMANN 2,707,223

ELECTRIC RESISTOR Filed June 15, 1949 2 Sheets-Sheet l F 37 1g4 I O 0Fig./ 36 7. kn

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INVENTOR. .HANS E. HOLLMANN TTORNEYS April 6, 1955 H. E. HOLLMANN2,707,223

ELECTRIC RESISTOR Filed June 15, 1949 2 Sheets-Sheet 2 lgUTPUT Fig. /0

IN PUT INVENTOR.

HANS E. HOLLMANN BY 4 i zs-w bm United States Patent ELECTRIC RESISTORHans E. Hollmann, Camarillo,

United States of America as retary of the Navy Calif., assignor to therepresented by the Sec- This invention concerns polar mixtures of afluid, semifluid, or solid state of aggregation, consisting of aninsulating and originally fluid or semi-fluid carrier material mixedwith semi-conductive particles whose dielectric constant differssubstantially from that of the carrier material. Such a mixture, whensubjected to an electric polarizing field, even when thickening,solidifying, or coagulating during this treatment, assumes an electricover-all conductivity which is nonlinear, i. e. which depends on themomentary polarizing field strength. The invention is more particularlyconcerned with the uses of such nonlinear mixtures in various fields ofelectric engineering. The interspace between a plurality of electrodesis filled with the fluid or semi-fluid mixture or a plurality ofelectrodes is immersed or embedded in the coagulating mixture, so thatthere results a non-linear resistor which can be controlled by externalor internal signals; such as additional electric or magnetic fieldsignals, mechanical, vibrational, strain, compressional, bending forces,turbulent signals applied or produced in the liquid carrier material,electromagnetic radiation signals, impinging particles signals, orcombinations of such signals.

An object of the present invention is to provide a nonlinear polarmixture wherein the overall conductivity of the mixture may becontrolled by external or internal signals of various types applied tothe polar substance thereof.

Another object is to provide a nonlinear resistor wherein the resistancethereof varies nonlinearly with respect to the voltage impressedthereon.

A further object of the invention is to provide polar tubes utilizing apolar mixture and operating in a manner similar to corresponding vacuumtubes.

These and further objects and aspects of the invention will become moreapparent through the following description, taken with reference to theaccompanying drawings which are intended to be illustrative only of thebroader principles underlying the invention. Since the peculiarproperties of the polar resistors seem to contradict common conceptions,it may be emphasized that the invention is the result of extensiveresearch carried on for many years and that its versatility issatisfactorily proven by numerous experiments. In order to disclose thebroad scope of the invention, it may be noted that the invention opensan entirely new field of electrical engineering, most of which,heretofore, has been confined exclusively to electronics.

Before describing the various forms of the instant invention in greaterdetail, it is necessary to explain the basic properties of the polarmixtures on which the invention is based. The polar mixture, accordingto the invention, is ranged in between two well known suspensions,namely the Magnetic Oil (Technical News Bulletin of the National Bureauof Standards volume 31, pp. 5460, 1948) on the one side and theElectrostatic Oil (U. S. Patent 2,417,850) on the other side. Since thecolloidal suspension is the easiest to describe and comprehend, it isgiven below in preference to polar fluids or substances which are basedon the same philosophy.

Figure 1 shows the irregular distribution of dielectric particles in aneutral suspension;

Figure 2 indicates the formation of dielectric chains resulting when thesuspension is subjected to a polarizing field;

Figure 3 shows the incremental voltage drop along the dielectric chains;

Figures 4, 5, and 6 indicate suitable electrode arrangements of polarresistors;

Figures 7 and 8 are typical characteristic explanations of the functionand operation of the invention;

Figure 9 indicates a polar triode; and

Figure 10 shows a modification in the form of a polar beam tetrode.

The polar fluid, suspension, mixture, or substance, according to theinvention, consists of an insulating and more or less viscous carriermaterial in which fine powder of semi-conductive particles is suspended,preferably in colloidal dispersion. This carrier material may be aninsulating oil, e. g. transformer oil, transformer insulating fluids,mineral oils, such as olive oil, castor oil, or silicone oils.Furthermore, the carrier material may consist of insulating pastes suchas Vaseline and other greases. Finally, the carrier material may befluid or semifluid only at the beginning of the production of a polarmixture, solidifying or coagulating, after intermixing of the powder,either by cooling, evaporation, polymerization, or chemical reaction.For example, there may be used paraflin or waxes, glues such as the wellknown household-cement, kaurite-glue, or resins, the best of which isacrylate-resin, or finally ordinary rubber which polymerizes under theinfluence of heat treatment.

The intermixed powder, in addition to being semiconductive, must have adielectric constant which differs substantially from that of the carriermaterial. Powdered substances such as cuprous oxide (cuprite), Rochellesalt, coal, or ordinary graphite create the desired nonlinear effectswith more or less eflicient results. It is probable that some carriermaterials and other agents which are still untried will give even betterresults than any so far experimented with. This may be the caseespecially when using very high frequencies, where the high frequencyconductivity and dielectric constant, in connection with the depth ofinfiltration, play a decisive role.

A control of colloidal suspensions or even of rough mixtures isbasically known. As mentioned before, there exist two types, namely: theso-called Magnetic Oil and its counterpart in the field ofelectrostatics, the socalled Electrostatic Oil. Both are put toingenious uses by utilizing their increasing viscosity when subjected toa suitable control field: the magnetic oil to a magnetic field, and theelectrostatic oil to an electric field. The ferromagnetic particles ofthe magnetic oil become magnetized and the dielectric particles of theelectrostatic oil become polarized; both types of particles attract eachother and arrange themselves in the form of magnetic or dielectricchains. Regardless of the type of chains, the viscosity of bothsuspensions increases when subjected to their associated fields. Thisviscosity effect is utilized, in the prior art, for transferringmechanical forces or torques in a magnetic or electric viscosity clutch.

The polar mixture according to the instant invention fits between thesetwo previously known extremes. Whereas the viscosity effect requireseither ferroor paramagnetic particles in the one case, and dielectricparticles in the other case, the nonlinear mixture or substanceaccording to this invention requires semi-conductive particles whosedielectric constant differs substantially from that of the carriermaterial. For special purposes, namely for magnetic control, theparticles, in addition to their semi-conductivity and dielectricconstant, must be paramagnetic, so that a control of the dielectricchains can be achieved by means of an additional magnetic field. Apowder which has been found to operate very satisfactorily, isferri-ferro-oxide. The new mixtures, according to this invention,display a nonlinear conductivity under electric or magnetic fields, butonly slight variation in viscosity, contrary to the aforementionedextreme cases of the electrostatic and magnetic oils.

The process of the formation of dielectric chains is explained ingreater detail by means of the Figures 1, 2, and 3. Referring to Fig. l,the dielectric, semi-conductive particles 30, in general, aredistributed at random throughout the carrier material 31, undergoing arandom molecular movement. However, as soon as a direct or alternatingvoltage is applied across the two electrodes 32 and 33 in Fig. 2, i. e.as soon as the neutral mixture is subjected to a direct or alternatingelectric field (produced e. g. by the battery 34) the dielectricparticles 30 become polarized and form the chains shown in Fig. 2. Thischain effect produces an electric linkage or connection between theelectrodes 32-33 and makes the mixture semi-conductive. Since theconductivity of the particles can be obtained only at the expense of thedielectric constant, the polar mixtures display only a very weakviscosity effect (contrary to the prior art magnetic and electric oils,aforementioned), and noticeable mechanical moments or torque momentscannot be transferred with the mixture of the instant invention.

Once the virgin state of the polar mixture is affected at a certainthreshold field, or in other Words, once the mixture is converted fromits virgin state corresponding in Fig. 1 into its polarized state asshown in Fig. 2, the conductivity increases further with increasingfield strength. In a pure physical sense, the polar mixture assumes anonlinear conductivity, and the resistance between the electrodesbecomes nonlinear. This particular phenomenon may be explained byreference to Fig. 3. The semi-conductivity of the dielectric particleseffects an incremental voltage drop along each individual chain in sucha way that the partial fields appear preponderantly in steps at thetransition resistances between every two particles whereas theconductivity of the particles prevents higher voltage drops across theparticles themselves. On the other hand, the dielectric constant of theparticles must have a certain minimum value for assuring an initialchain formation. Consequently, the dielectric constant and conductivityof the particles on one hand, and the dielectric constant of the carriermaterial on the other hand assume great significance for obtaining thedesired nonlinearity effect. Furthermore, the high electric fieldscreated in the transition regions, where the particles touch each other,produce strong electrostatic forces of attraction. As a result, thedielectric chains are reinforced at increasing field strength orelectrode voltage so that the increasing over-all conductivity may beconsidered as being caused by the action of innumerable fluctuatingcontacts between the innumerable links. An important result of thiselectrostatic attraction is a very high frequency response evenextending into the microwave range.

One practical example of the polar resistor, namely two flat or evencylindrical electrodes, has already been shown in Fig. 2. The simplestform, however, consists of a drop of the polar mixture suspended betweentwo closely situated wire electrodes by adhesion only. Another exampleconsists of a glass tube closed at both ends and occupied by the polarmixture or substance. A wire electrode is immersed in each sideextending into the polar mixture or substance. Varying the gap betweenthe wires or varying the entire length of the glass tube permits theresistance to be changed within very large limits and to a be matched toany desired voltage range.

Aside from the electrode separation, which determines the voltagesensitivity or nonlinearity, the power dissipation can be adjusted byvarying the surface of the electrodes. A very practicable type of polarresistor is indicated in Fig. 4. Two wires 35 and 36 are wound bifilarlyon a supporting member 37 of mica, Plexiglas, ceramic, or other suitableinsulator of any arbitrary shape. The entire device is immersed in asuitable container filled with the liquid mixture. Another modificationis obtained by covering the electrode arrangement with a thin layer ofthe liquid mixture, after which the entire device can be wrapped withinsulating or Scotch tape.

Referring to Fig. there is shown another modification of a polarresistor which resembles a mica capacitor. It comprises two sets of foilelectrodes 38 and 39 with insulating sheets 40, e. g. of mica,inbetween. These mica sheets are perforated and the perforations arefilled with the polar mixture before assembling.

If a high voltage sensitivity at relatively low power dissipation isrequired, the polar resistor shown in Fig. 6 is convenient. It comprisesa glass mirror 41 whose silver layer is cut with a sharp knife or razorblade, so that two electrodes 42 and 43 result with a minute gap of onlya few thousandths of an inch. This very fine gap is bridged by a drop ofthe polar mixture and is protected by a small piece of mica before theentire resistor is wrapped with tape. Various modifications can bederived from the three types shown in Figs. 4, 5, and 6.

Until now, the polar mixture according to the invention has beendescribed preponderantly as a liquid, semiliquid, or more or less in aconsistent state of aggregation. A further improvement is obtained byconverting the liquid or consistent mixture into a solid state thuschanging all previously described examples of polar resistors into drytypes.

The simplest way to produce such dry resistors is by means of wax suchas paraffin. The paraffin is heated in a container until it melts. Then,a certain amount of graphite powder, for instance 20 per cent by volume,is intermixed and carefully stirred up. One of the electrodearrangements described before is immersed into the hot paraflin-graphitesuspension or the hot mixture is poured over the electrode arrangementsshown in Figs. 4 and 6. Since the high temperature does not disturb thechain formation, the hot resistor is formed just as the previous coldresistors with the aid of an electric polarizing field between itselectrodes. The paraffin cools slowly under the continuous influence ofthe electric field so that the electric nonlinearity is retained untilthe paraffin reaches its solid state, i. e. until it becomes dryparaflin intermixed with graphite. In this manner an artificial polarsubstance and dry polar resistors can be produced.

During the cooling and coagulating of the hot paraffin, the over-allconductivity and, at the same time, the electric nonlinearity decreasesconsiderably because the paraffin shrinks. This shrinking effect causesthe dielectric chains to be compressed so that the frozen mixture isunder an internal compressional bias.

This disadvantage can be avoided by utilizing a carrier material whichcoagulates without shrinking or evaporation. Liquids with this specialproperty are, e. g. kauriteglue, Khotinsky-cement, and acrylate resin.All these substances are composed originally of two separate fluidswhich, after being intermixed, solidify due to chemical reactionswithout noticeable shrinking. Consequently, a polar substance and drypolar resistors can be produced by intermixing the semi-conductivepowder with one of the initial solutions and slowly adding the bindingreactor until the combined suspension, while under the continuousinfluence of a polarizing field, becomes completely hard, similar to thecold parafiin mixture. The hardening process of such polar resistors isconsiderably accelerated if the polarizing field is produced by means ofhigh frequency voltages which, at the same time, produce a diathermyfield accelerating the chemical binding reaction.

Another carrier material which assures a well pronounced electricnonlinearity and, furthermore, particular applicability, is rubber. Apolar rubber is produced, according to the invention, by intermixing thesemi-conductive, dielectric powder with liquid rubber and bypolymerizing this liquid mixture by heat while under the continuousinfluence of a sufficiently strong polarizing field. Although theaforementioned polar substances show a more or less pronouncedsensitivity to vibrational or compressional forces, the polar rubberwith its included semi-conductive chains, because of its elasticity, ismuch more sensitive to any compression or dilation, because togetherwith the rubber the incorporated chains are compressed or extended. As aresult, the over-all conductivity increases or decreases to a very highamount by compressing or extending the polar rubber.

All practical requirements concerning power dissipation and voltagesensitivity can be fulfilled by selecting and adjusting the size of thesupporting member or the surface of the electrodes, respectively, andthe distance inbetween.

The electric function of the polar resistor, or, more generally, of thepolar mixture or substance, is disclosed in the characteristics shown inthe qualitative Figures 7 and 8. If a direct or alternating voltage isimpressed upon the two electrodes of a polar resistor, either in liquidor dry form, the passing current increases nonlinearly with increasingvoltage thus yielding nonlinear transfer characteristics of the formindicated in Fig. 7. Since the polarity is of no consequence, thecharacteristic is symmetrical. The polar resistance changes from acertain zero value R0, characterized by the slope of the dotted initialtangent in the zero point, to a very much lower saturation value Rs,characterized by the dashed end-tangent. At this extreme state ofsaturation all links c ntribute to the saturation conductivity becausethey all are strongly pressed together along all chains. For the sake ofcompleteness it must be emphasized that the full state of saturation,under practical conditions, cannot be reached but only approachedbecause the oil becomes overloaded and unstable.

The nonlinear transition between R0 and Rs is more clearly disclosed bythe nonlinear resistance characteristic shown in Fig. 8. It is obtainedby plotting the voltageto-current ratio V/I=R against the appliedvoltage V. A more general physical picture is obtained by consideringthe conductivity in relation to the polarizing field E= V/e=V where e isthe electrode gap, under the present assumption of setting e: 1.

In addition a differential resistance Rdifi must be taken intoconsideration whenever the polar resistance is controlled by analternating voltage superimposed on a certain bias. Obviously thedifferential resistance also is nonlinear.

Without going into further details it may be mentioned that RS dependsprimarily on the conductivity of the particles as well as on the mixtureratio. hand R0 and the transition region is determined not only by thepure electric properties of the polar mixture or substance but also byits previous history, which means, by the momentary state of the chainsas they are formed under the influence of a certain bias or alternatingvoltage. This effect may be compared roughly to the peculiar behavior offerromagnetics and polar dielectrics displaying Rochelle-salt propertiesespecially in its virgin state, and hysteresis.

In order to distinguish the polar resistor over well known devices, itmay be mentioned that it has a certain analogy to the obsolete coherer.However, whereas the latter operates, so to speak, only as an off-ondevice because its resistance fluctuates only between infinity and zero,the polar resistor displays a shaded transition between R0 and Rs. Aslong as RS is not attained, the polar resistor requires no externalreduction to its initial condition as is necessary for the coherer bymeans of mechanical shocks. Only under special conditions, namely whenthe polar resistors become overloaded, do the dielectric particles fusetogether, just as do the metal particles in the coherer. In this specialcase the welded chains remain intact even at decreasing fields and canbe destroyed only by stirring up the mixture or by strong vibrations.Once the dry paraffin resistor is overloaded, it must be heated again orsubjected to even stronger overloading currents until the paraffinmelts, so that a new chain formation can be accomplished. The completelydry resistors, made of Kaurit, acrylate or rubber, cannot be repaired,once damaged by overloading.

On the basis of this new philosophy many practical applications areobvious to one skilled in the art. All applications are based on theimportant phenomenon that the linkage strength of the dielectric chainsand, therefore the over-all conductivity, can be controlled by externalor internal signals of various types applied to the polar substance orsuspension. In general such signals may be of one or more of thefollowing forms: additional electric or magnetic fields, mechanicalvibrations or strains, compressional or bending forces, sound orsupersonic waves, turbulences in the fluid mixture caused by a stream ofthe latter or by moving electrodes, electromagnetic radiation covering alarge portion of the whole spectrum, or impinging particles. It istherefore apparent that many types of transducers may be constructedutilizing an electrically nonlinear polar mixture according to thepresent invention.

In contrast to all previously known devices operating with various typesof colloidal suspensions, i. e. with magnetic or electrostatic oil, thechange in resistance, according to this invention, producescorresponding fluctuations of the direct or alternating currents flowingthrough the polar resistor in series with a load impedance.

According to the invention a further feature is that the dielectricchains are controlled by the aid of additional electric control fieldswhich are generated between auxiliary control electrodes and the outputelectrodes, or only between two or more control electrodes. Referring toFig. 9, the simplest device for obtaining a pure electrical control,similar to that of a vacuum triode, contains two output electrodes,which, in analogy to a vacuum triode, may be called cathode 118 andanode 119. The grid electrode 120 is arranged between both mainelectrodes and the entire interspace is occupied by the polar mixture inliquid or in dry form. Provided the over-all conductivity of the polarmixture,

On the other I depending on the substance of the dielectric particles,the mixture ratio, and the chain-forming plate field, is not so highthat a noticeable control field around the grid is neutralized orsuppressed-a condition resembling the existence of a very high spacecharge in a vacuum tube-the chains extending between cathode 118 andanode 119 are strengthened or weakened under the influence of thefluctuating grid fields. As a result the liquid triode has a mutualtransconductance similar to that of an electronic tube, although thiscomparison is subjected to certain limitations. However, favorableoperational conditions, such as suitable electrode separations, mixtureratios, etc., assure an over-all performance largely analogous to avacuum triode so that the latter for many purposes, can be replaced byliquid triodes. The simplicity of its construction, i. e., no thermionicemission and no vacuum, gives the polar tubes an overwhelmingsuperiority over the electronic tubes in many respects, especially sosince not only small and sensitive tubes but also big power tubes can bemanufactured at very low cost.

It is to be noted primarily, that the theory and behavior of the polartubes differs in several respects from that of vacuum tubes which dependon their freely operating electrons. An important feature is the platereaction resulting from the nonlinearity of the plate resistance.Consequently, the alternating output voltages, in relation to the directplate supply voltage, are limited because intolerable distortions wouldotherwise occur in the plate circuit. A low-impedance plate load, therefore, is preferable. If a high voltage amplification is to be obtained,a step-up transformer 121 (Fig. 9) may be used similar to theaforementioned polar detector and polar transducer. A regenerativefeed-back, i. e. the output voltage leading back to the grid,immediately produces a polar oscillator whose frequency is determined inthe usual manner by a tuned-plate and/or a tuned-grid circuit.

Fig. 10 differs from Fig. 9 by transversal control fields beinggenerated between interleaved grids 122 and 123 which are fed inpush-pull by the center-tapped input transformer 124. The grid wires, atthe same time, may be shielded by insulating strips 125 against cathodeand anode so that the effective chains extend throughout the interspacebetween these strips. The grid bias is permitted to adjust automaticallyby means of the capacitor 126 in accordance with the direct voltage dropbetween cathode and anode. This results in a type of a polar beamtetrodewhose current lines, represented by the dielectric chains, areconcentrated preponderantly in a transverse direction. The power gain ofsuch a polar beam-tetrode considerably exceeds that of the simple polartriode.

As can be seen by means of these few examples the invention opens thefield for a completely new technique in liquid or even dry tubes whosedesign and performance can be taken from current electronic practice.

As noted previously, the bipolarity of the colloidal resistor makesdirect rectification impossible. However, a power rectification can beobtained by means of polar tubes together with auxiliary rectifiers suchas selenium rectifiers or thyratrons, etc. which control the gridpotential in such a manner that the polar tube is closed only duringone-half cycle. In this way, one or more polar tubes operate only ashigh power relays whereas only small rectifiers are required forproducing the desired grid control. In connection with the foregoingdescriptions and explanations this procedure is well understood inanalogy to common rectifier technique.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

l. A nonlinear resistor having a plurality of spaced electrodes, theinterspace being occupied by a polar mixture which consists essentiallyof an insulating carrier material and semi-conductive particles whosedielectric constant differs substantially from that of said carriermaterial, the particles being effective under the influence of apolarizing electrostatic field to become polarized and thereby toarrange themselves in the form of semi-conductive chains electricallylinking said electrodes.

2. A nonlinear resistor which comprises a plurality of spacedelectrodes, the interspace being occupied by a polar mixture whichconsists essentially of an insulating carrier material andsemi-conductive particles suspended therein in the form ofsemi-conductive chains electrically linking said electrodes, saidparticles having a dielectric constant differing substantially from thatof said carrier material.

3. A nonlinear resistor as defined in claim 2, said carrier material isan insulating fluid.

4. A nonlinear resistor as defined in claim 2, said carrier material isan insulating solid.

5. A nonlinear resistor as defined in claim 2, said carrier material isresilient.

6. A nonlinear resistor as defined in claim 2, said carrier material isacrylate resin.

7. A nonlinear resistor as defined in claim 2, wherein saidsemi-conductive particles are graphite particles.

8. A transducer which comprises a nonlinear resistor having a pluralityof spaced electrodes, the interspace being occupied by a polar mixturewhich consists essentially of a solid insulating carrier material andsemi-conductive particles embedded therein in the form of semiconductivechains electrically linking said electrodes, said particles having adielectric constant differing substantially from that of said carriermaterial.

wherein wherein wherein wherein 9. An electrical device which comprisesa nonlinear resistor having a pair of spaced electrodes, the interspacebeing occupied by a polar mixture which consists essentially of aninsulating carrier material and semi-conductive particles suspendedtherein in the form of semi-conductive chains electrically linking saidelectrodes, and a third electrode in said mixture intermediate said pairof spaced electrodes, said particles having a dielectric constant1differing substantially from that of said carrier materia ReferencesCited in the file of this patent UNITED STATES PATENTS 1,325,889 Curtisa- Dec. 23, 1919 1,822,742 McEacheron Sept. 8, 1931 1,919,053 BrintonJuly 18, 1933 1,989,187 Fitzgerald Jan. 29, 1935 2,418,516 Lidow Apr. 8,1947 2,469,569 Ohl May 10, 1949 2,500,953 Libman Mar. 21, 1950 2,532,157Evans Nov. 28, 1950 FOREIGN PATENTS 22,142 Great Britain of 1901

